Identification of a molecular marker linked to apomixis in Brachiaria humidicola (Poaceae)

Abstract

A bulked segregant analysis using RAPD technique was carried out to identify molecular markers linked to apomixis in a Brachiaria humidicola F 1 population that segregated 1 : 1 for the mode of reproduction (apomixis and sexual). A marker related to the apo-locus was found. Segregation data, together with this marker were used to generate a map of the region. This marker was located at 4.61 cM of the target locus, and it can be used in deploying marker-assisted selection for mode of reproduction in the hybrid progenies of this species.Brazil is the worldÕs largest beef exporter and also has the biggest cattle herd, numbering about 200 million heads. This large herd feeds almost exclusively on pastures. Cultivated pastures in Brazil cover an estimated 120 million ha, and about 85% of this area is planted to Brachiaria species (Macedo 2006). This paper describes the work carried out with a hybrid population of B. humidicola (Rendle) Schweickert, also known as koronivia grass, a perennial savanna grass native to Africa. This species is well adapted to poorly drained and infertile acid soils (Keller-Grein et al. 1996). Most B. humidicola ecotypes are polyploid and reproduce by apomixis, an asexual mode of reproduction through seeds (do Valle and Savidan 1996).Apomixis in B. humidicola is facultative, pseudogamous and embryo sacs show apospory of the Panicum type, where the apospore develops into a diploid, monopolar four-nucleate embryo sac with a three-celled egg apparatus and a central cell with one nucleus (Savidan 1982). Pseudogamy means that for endosperm development the secondary nucleus of the embryo sac needs to be fertilized by a male gamete (Alves et al. 2001). Facultative apomictic plants develop both aposporous and meiotic sacs within the same inflorescence and even within the same pistil (Nogler 1984). The two reproductive modes are not mutually exclusive, therefore, some segregation may be observed in the progeny of an apomictic Brachiaria genitor.In the main Brachiaria species apomixis is simply inherited (do Valle and Savidan 1996), thus apomictic and sexual hybrids are generated at each sexual · apomictic cross in the proportion of 1 : 1.The objective of this work was to identify RAPD markers tightly linked to apomixis in B. humidicola hybrids to improve efficiency and accuracy in the determination of the reproduction mode on the breeding programme of this species. Materials and MethodsPlant material: One hundred and seven plants belonging to an F 1 population obtained by crossing a polyploid apomictic cultivar (B. humidicola cv. BRS Tupi) with a polyploid sexual parent (BRA005811-H31) were analysed. The hybrid nature of the F 1 plants was confirmed using RAPD markers.Analysis of mode of reproduction: Flowers of these hybrids were collected at anthesis. Sixty ovules were dissected from each hybrid and then clarified using methyl salicylate according to the Young et al. (1979) procedure. At least 50 cleared ovules were analysed per plant using an interference contrast microscope. A chi-squared test w...

Genetic divergence among Brachiara humidicola (Rendle) Schweick hybrids evaluated in the Western Brazilian Amazon

“…However, only recently, crosses were made between cultivar BRS Tupi and sexual accession H031, both hexaploid (2n=6x=36), which led to the development of 364 full-sib progenies (Figueiredo et al 2012), segregating in a proportion of 1:1 for reproduction mode (sexual and apomictic) (Zorzatto et al 2010). These sexual and apomictic hybrid progenies were evaluated and selected in Campo Grande and 14 were sent to Acre for testing under the soil-climatic conditions of the Western Brazilian Amazon.…”

Molecular markers linked to apomixis in Panicum maximum Jacq.

“…This technique showed to be efficient in the apomictic species Brachiaria sp. (Pessino et al, 1997), Pennisetum squamulatum (Ozias-Akins et al, 1998), Poa pratensis (Barcaccia et al, 1998), Paspalum simplex (Labombarda et al, 2002;Gualtieri et al, 2006), P. maximum (Ebina et al, 2005), Cenchrus ciliaris (Gualtieri et al, 2006;Yadav et al, 2012), Hypericum perforatum (Barcaccia et al, 2007;Schallau et al, 2010), and Brachiaria humidicola (Zorzatto et al, 2010), among others.…”

Meiotic behavior in nonaploid accessions of Brachiaria humidicola (Poaceae) and implications for breeding

“…Hybridization was accomplished and some promising hybrids are under agronomic evaluation ). The progeny segregated in a 1:1 proportion in sexual and apomictic hybrids (Zorzatto et al, 2010). Apomixis is desirable in the breeding program, since it fixes the selected interesting agronomic characteristics through the production of clonal seeds.…”